There are people who are so greedy, they can't stand the thought of losing a deal and having someone else get the game. So they queer the deal by offering the seller more money and telling them the other buyer is cheating them.
Buyers like this stink and should stay out of the mix. I have no problem with them saying if the other deal falls through, I'll take the game sight unseen. But to over bid someone else just to be the one to get the game is unethical .
Also, it's not my job to educate a seller. If they're too lazy to look on craigslist or Ebay to get a range of prices, thats their problem. Unless its someone elderly or in some reduced capacity where I feel I would be taking unfair advantage of them, then I might give them an unsolicited higher offer. But not if they're too rich to care or too lazy to look. Then I take a good deal. And because I got it cheap, I can let it go cheaper to the next guy. Can't do that if someone else pushes me to the absolute max by butting in with a higher offer.